1. Field of the Invention
The present invention relates to an image data storage/processing apparatus which is particularly applicable to an electronic still camera, for example.
2. Description of the Related Art
For example, a digital electronic still camera is a camera device in which a solid state image pick-up device such as CCD is used to capture a field, and an image signal representative of the thus captured object image is finally stored in a memory in the form of digital data. In general, as the memory, there is used such a memory card type of memory to which a RAM (Random Access Memory), such as a semiconductor memory, is mounted. In this case, in order to efficiently use storage areas of the memory, data compression such as orthogonal transformation encoding is often performed.
Particularly, the orthogonal transformation encoding has been generally employed, since it is possible to perform encoding in a large compression ratio, and also to suppress an image distortion brought by the encoding.
In the digital electronic still camera, if it is important for a memory, such as a frame memory, to temporarily store image data representative of a field to be recorded in consideration of cost, then it would be preferable to use a DRAM (Dynamic RAM). According to such a DRAM, however, when the DRAM is accessed in conjunction with an image data processing, a time exists when it is not permitted to actually output the image data, such as the time required for setting of a row address, pre-charging of electric charge the capacitor of each memory cell which is performed in a predetermined period of time, and so on.
In the digital electronic still camera, on the other hand, as a matter of convenience for image processing, such as a bidimensional orthogonal transformation, etc., which is performed after the image data is read out from the frame memory, it is preferable, in units of block constituting the bidimensional orthogonal transformation to continuously output the image data from the frame memory to the successive image processing circuit.
In an electronic still camera having a reproducing function as well as a recording function, an image signal recorded on a recording medium is read out, expansion-decoded and reproduced on a display device. In such an electronic still camera for use in both the recording and the reproducing, it is necessary to convert an image picked up in the form of a field image signal by an array of photosensitive cells of the image pick-up device, for example, into a frame image signal prior to a compression processing. Consequently, it is necessary to temporarily store the image signal in a memory and read out it in the form of the frame image signal.
Also, it is required for a YC processing circuit to perform such a processing that a luminance signal Y and a color difference signal R-Y, B-Y are produced from the image signal according to the array of photosensitive cells of the image sensor read out in the form of the frame image signal. The luminance signal Y and the color difference signals R-Y, B-Y produced by the YC processing circuit are again stored in the memory and thereafter are compression-encoded. In the compression-encoding, an image field of data is divided into a plurality of blocks to perform the compression-encoding, and thus it is necessary to control readout from the memory so as to permit the readout of every block.
Further, also in a case where the image signal read out from the recording medium is expansion-decoded, it is necessary to temporarily store the image signal in a memory and read out the image signal therefrom, since the plurality of blocks are combined to restore the original image field of the signal. Furthermore, in a case where a reproducing circuit performs such a processing that the decoded image signal is reproduced on the display device, it is necessary to control readout of the decoded image signal.
As mentioned above, it was necessary to perform operations of readout or writing of the image signal from or into the memories on various types of image data and thus a plurality of memories were needed, since controls for the readout and the writing are varied on the respective types of image data.